A portion of the disclosure of this patent document contains material which is subject to copyright protection. The owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
This invention uses ramjet technology for power generation. The fundamentals the technology were set forth in detail in my prior application Ser. No. 07/945,228, filed Sept. 14, 1992, now U.S. Pat. No. 5,372,005, issued Dec. 13, 1994. Certain embodiments were also provided in U.S. patent application Ser. No. 08/480,663, filed Jun. 7, 1995, now U.S. Pat. No. 5,709,076, issued Jan. 20, 1998. Specific embodiments were also earlier disclosed in my U.S. Provisional Patent Application, Ser. No. 60/028,311, filed Dec. 16, 1996. The disclosures of such patent applications, and the issued U.S. patents, all as just indentified in this paragraph, are incorporated herein by this reference.
This invention is based on, and the benefit of priority under 35 U.S.C. Section 119(e) is claimed from, U.S. Provisional Patent Application No. 60/089,674 filed Jun. 17, 1998.
My invention relates to a high efficiency, novel ramjet driven rotary engine, and to a method for the generation of electrical and mechanical power with the engine, while minimizing emission rates of nitrogen oxides. More particularly, my invention relates to a power plant driven by a ramjet engine, and to structures which are designed to withstand the extremely high tensile stress encountered in a rotating device with distally located ramjets operating at supersonic speeds. Power plants of that character are particularly useful for generation of electrical and mechanical power.
A continuing demand exists for a simple, highly efficient and inexpensive thermal power plant which can reliably provide low cost electrical and mechanical power. This is because many electrical and/or mechanical power plants could substantially benefit from a prime mover that offers a significant improvement over currently practiced cycle efficiencies in power generation. This is particularly true in medium size power plantsxe2x80x94largely in the 10 to 100 megawatt rangexe2x80x94which are used in many industrial applications, including stationary electric power generating units, rail locomotives, marine power systems, and aircraft engines.
Medium sized power plants are also well suited for use in industrial and utility cogeneration facilities. Such facilities are increasingly employed to service thermal power needs while simultaneously generating electrical power at somewhat reduced overall costs. Power plant designs which are now commonly utilized in co-generation applications include (a) gas turbines, driven by the combustion of natural gas, fuel oil, or other fuels, which capture the thermal and kinetic energy from the combustion gases, (b) steam turbines, driven by the steam which is generated in boilers from the combustion of coal, fuel oil, natural gas, solid waste, or other fuels, and (c) large scale reciprocating engines, usually diesel cycle and typically fired with fuel oils.
Of the currently available power plant technologies, diesel fueled reciprocating and advanced aeroderivative turbine engines have the highest efficiency levels. Unfortunately, with respect to the reciprocating engines, at power output levels greater than approximately 1 megawatt, the size of the individual engine components required become almost unmanageably large, and as a result, widespread commercial use of single unit reciprocating engine systems in larger sizes has not been developed. Gas turbines perform more reliably than reciprocating engines, and are therefore frequently employed in plants which have higher power output levels. However, because gas turbines are only moderately efficient in converting fuel to electrical energy, gas turbine powered plants are most effectively employed in co-generation systems where both electrical and thermal energy can be utilized. In that way, the moderate efficiency of a gas turbine can in part be counterbalanced by using the thermal energy to increase the overall cycle efficiency.
Fossil fueled steam turbine electrical power generation systems are also of fairly low efficiency, often in the range of 30% to 40% on an overall net power output to raw fuel value basis. Still, such systems are commonly employed in both utility and industrial applications for base load electrical power generation. This is primarily due to the high reliability of such systems.
In any event, particularly in view of reduced governmental regulation in the sale of electrical power, it can be appreciated that significant cost reduction in electrical power generation would be desirable. Fundamentally, particularly in view of long term fuel costs, this objection can be most effectively accomplished by generating electrical power at a higher overall cycle efficiency than is currently known or practiced.
I have now invented an improved power plant based on the use of a supersonic ramjet as the prime mover to rotate a power shaft. In using this method to generate electrical power, the supersonic ramjet is directly or indirectly coupled with an electrical generator. By use of a metered fuel feed arrangement, the power output of the ramjet can be turned down as necessary to maintain constant rotating velocity, such as is necessary in synchronous power generation apparatus, at minimal output loads. Throughout its operating range, the supersonic ramjet power plant has greatly increased efficiencies when compared to those heretofore used power plants of which I am aware.
The designs incorporated into my power plant overcomes four significant and serious problems which have plagued earlier attempts at ramjet utilization for efficient electrical power production:
First, at the moderate mach number tip speeds at which my device operates (preferably, Mach 2.5 to about Mach 4.0), the design minimizes aerodynamic drag. This is accomplished by both reducing the effective atmospheric density that the rotor encounters, and by use of a boundary layer control and film cooling technique. Thus, the design minimizes parasitic losses to the power plant due to the drag resulting from rotational movement of the rotor. This is important commercially because it enables a power plant to avoid large parasitic losses that undesirably consume fuel and reduce overall efficiency.
Second, the selection of materials and the mechanical design of rotating components avoids use of excessive quantities or weights of materials (a vast improvement over large rotating mass designs), and provides the necessary strength, particularly tensile strength where needed in the rotor, to prevent internal separation of the rotor by virtue of the centrifugal forces acting due to the extremely high speed rotor.
Third, the design provides for effective mechanical separation of the cool entering fuel and oxidizer gases from the exiting hot combustion gases, while allowing ramjet operation along a circumferential pathway.
Fourth, the design provides for effective film cooling of rotor rim components, including rim segments, rim strakes, and ramjet thrust modules. This novel design enables the use of lightweight components in the ramjet combustor and in the ramjet hot combustion exhaust gas environment.
To solve the above mentioned problems, I have now developed novel rotor designs which overcome the problems inherent in the heretofore known apparatus and methods known to me which have been proposed for the application of ramjet technology to stationary power generation equipment of primary importance, I have now developed a low drag rotor having an axis of rotation, and which has one or more unshrouded ramjet thrust modules rotatably mounted on the distal edge thereof. A number N of peripheral, preferably partially helically extending strakes S partition the entering gas flow sequentially to the inlet to a first one of one or more ramjets, and then to a second one of one or more ramjets, and so on to an Nth one of one or more ramjets. Each of the strakes S has an upstream or inlet side and a downstream or outlet side. For rotor balance and power output purposes, I prefer that the number of ramjets X and the number of strakes N be the same positive integer number, and that N and X be at least equal to two. More preferably, I find it desirable that N and X be equal to five. The exhaust gases exiting from each of the one or more ramjets is effectively prevented from xe2x80x9cshort circuiting,xe2x80x9d or returning to the inlet side of subsequent ramjets. In the area of each ramjet combustor, this is effectively accomplished by the strakes S, due to overpressure in the ramjet combustor. Downstream from the ramjet exhaust area, and extending until just before the inlet to the next of the one or more ramjets, the prevention of bypass of the hot exhaust combustion gases to the cool entering fuel air mixture is effectively accomplished by the design of my one or more ramjet thrust modules, as it is preferred that the exhaust gases from each ramjet be expanded to approximately atmospheric pressure, so the strakes S merely act as a large fan or pump to move exhaust gases along with each turn of the rotor.
I have provided several embodiments for an acceptable high strength rotor. In a preferred embodiment, the rotor section comprises a carbon fibre disc. In another , it comprises a steel hub with high strength spokes. In each case, rim segments and ramjet thrust modules are preferably releasably and replaceably affixed to the rotor.
A rotor operating cavity is provided, at least part of which has a lowered atmospheric pressure, preferably in the 1 psia range, in order to eliminate aerodynamic drag on the rotor. The vacuum conditions are assured by use of a vacuum pump to evacuate the operating cavity, and by the use of appropriate seals (a) at the rotor output shaft where it penetrates the operating cavity walls (b) at the rim segments, and (c) at the ramjet thrust modules.
The rim segments and the ramjet thrust module each include a cooling air receiving chamber. The chambers each have radially extending, preferably substantially parallel sidewalls, a radially proximal wall, and a radially distal wall, through which cooling gas outlets penetrate. Such outlets may be cylindrical orifices, or slots, or other desirable shapes. The cooling air receiving chamber functions as a centrifugal compressor for delivery of cooling gas to cooling gas outlet orifices. The exit of the cooling gas orifices is located on the surface of the rim segments and the ramjet thrust modules. The radial dimension at the start of each individual air receiving radially proximal wall determines the distance over which that air receiving chamber operates for compression, and thus determines the pressure of air delivered at the exit of a particular boundary layer cooling outlet orifice.
Attached at the radial end of the rotor are one or more of the at least one ramjets, each ramjet preferably having an unshrouded thrust module construction. The ramjet engines are situated so as to engage and to compress that portion of the airstream which is impinged by the ramjet upon its rotation about the aforementioned axis of rotation. Fuel is added to the air before compression in the ramjet inlet. The fuel may be conveniently provided through use of fuel supply passageways located in an annular ring, with fuel injection passageways communicating between the fuel supply passageways and the inlet air passageway. Fuel injected into the inlet air stream is thus well mixed with the inlet air before arriving at the ramjet engine combustion chamber. The combustion gases formed by oxidation of the fuel escape rearwardly from the ramjet nozzle, thrusting the ramjet tangentially about the axis of rotation, i.e., about the output shaft portions, thus turning the rotor and the coupled output shaft portions. The power generated by the turning output shaft portions may be used directly in mechanical form, or may be used to drive an electrical generator and thus generate electricity. The operation of my ramjet engine may be controlled to maintain synchronous operation, i.e., vary the power output from the ramjet, while maintaining constant speed shaft operation.
When the ramjet power plant is used in a co-generation configuration, the exhaust combustion gases from the ramjet are transported to a heat exchanger, where the gases are cooled as they heat up a heat transfer fluid (such as water, in which case the production of hot water or steam results). The heat transfer fluid may be utilized for convenient thermal purposes, or for mechanical purposes, such as for driving a steam turbine. Ultimately, the cooled combustion gases are exhausted to the ambient air.
Finally, many variations in the air flow configuration and in provision of the fuel supply, secondary fuel supply, and in providing startup ignitors, may be made by those skilled in the art without departing from the teachings hereof. Finally, in addition to the foregoing, my novel power plant is simple, durable, and relatively inexpensive to manufacture.
From the foregoing, it will be apparent to the reader that one important and primary object of the present invention resides in the provision of a novel ramjet powered engine which can be cost effectively used to generate mechanical and electrical power.
More specifically, an important object of my invention is to provide a ramjet driven power generation plant which is capable of withstanding the stress and strain of high speed rotation, so as to reliably provide a method of power generation at high overall efficiency.
Other important but more specific objects of the invention reside in the provision of power generation plants as described in the preceding paragraph which:
have high efficiency rates; that is, they provide high heat and high work outputs relative to the heating value of fuel input to the power plant;
in conjunction with the preceding object, provide lower power costs to the power plant operator and thus ultimately to the power purchaser than is presently the case;
allow the generation of power to be done in a simple, direct manner;
have a minimum of mechanical parts;
avoid complex subsystems;
require less physical space than many existing technology power plants;
are easy to construct, to start, to operate, and to service;
cleanly burns fossil fuels;
in conjunction with the just mentioned object, results in fewer negative environmental impacts than most power generation facilities presently in use;
have a rotating element with a minimal distally located mass structure, and which thus minimizes and therefore is able to withstand the stresses and strains of rotating at very high tip speeds; and which
provides for operation with minimal aerodynamic drag.
One feature of the present invention is a novel high strength rotor structure. In one design, a high strength steel inboard section is provided with high strength spokes that at their distal end suspend a rotating rim that has unshrouded ramjet thrust modules integrated therein. This unique structure enables operation at rotational speeds above stress failure limits of many conventional materials, while simultaneously providing for adequate cooling of the rim and ramjet structure, in order to maintain material integrity, at the high temperature operating conditions. In another design, a carbon fiber epoxy composite disc is provided, which simplifies the overall construction while providing an abundance of strength, while still providing a ventilated positive cooling system design to maintain structural integrity of the rotor, and of the rim and ramjet structure.
Another feature of the present invention is the use of a unshrouded ramjet design. In this design, a sturdy, stationary, peripheral wall which surrounds the rotating portion of the ramjet functions as part of the ramjet thrust module. This unique design enables use of a minimal rotating mass at the high design tip speeds, thereby enabling the rotor to be designed with lower strength materials and/or a higher margin of safety with respect to overall tensile strength requirements for a given ramjet operational mach number.
Still another important feature of the present invention is the use of strakes to partition the ramjet inlet air flow (and preferably in which inlet air flow the fuel and air are pre-mixed) from the ramjet exhaust gas flow. This elegant design feature assures that exhaust gases are directly removed from the engine, and that only the amount of inlet air necessary for combustion in the ramjets is required to be provided.
Finally, another important feature is the use of perforations in the strakes to minimize boundary layer buildup, (and accompanying drag) during high speed operation, by passing a small portion of pressurized gas thru such perforations to sweep away an otherwise stable boundary layer zone.
Other important objects, features, and additional advantages of my invention will become apparent to those skilled in the art from the foregoing and from the detailed description which follows and the appended claims, in conjunction with the accompanying drawing.